Testing a Automotive Style Coil with a DVOM is easy to do and is another diagnostic tool that you can put in your toolbox and another use for your DVOM.

Again the goal is to show the test procedure along with some insights into the operation of the coil.

The coil is in its simplest of forms a step up transformer. The coil converts system voltage from 6 or 12 volts at high amperage(this is called the primary circuit) to 20,000 to 30,000 volts at a low amperage (this is called the secondary circuit). The high secondary voltage has enough PUSH to jump the spark plug gap under compression pressure.

The coil primary circuit has a + (positive) terminal and a - (negative) terminal. The coil has to be wired into the circuit with the polarity. The correct polarity is needed so that the spark will JUMP from the spark plug center electrode to the ground tab. If the polarity is reveresed the spark JUMPS from the ground tab to the center electrode (most spark plugs are not designed to operate this way).

The correct coil polarity is determined by the battery ground. The points are the ground side of the primary circuit. 6 volt cubs are positive ground, so the positive terminal on the coil will be wired to the points.On the other hand if your vehicle is Negative ground (12 volt cubs) the negative terminal will be wired to the points.

In this test we are testing for internal shorts or high resistance that will prevent the coil from putting out it's 20,000 volt secondary spark. A good coil will range from 7,000 to 10,000 Ohms of resistance. This resistance value is one of those general rules of thumb that works for most coils.